Biologists Replay 500 Million Years Of E Coli Evolution In The Lab

September 27, 2012

Biologists Replay 500 Million Years Of E Coli Evolution In The Lab

Astrobiologists have recreated 500 million year-old bacteria then watched them evolve. The plan? To look for universal laws of biological evolution

Biology is changing so rapidly and fundamentally that it’s hard to keep track of the revolutionary transformations that are afoot.

Here’s one of them. Synthetic biology is the design and construction of biological systems not found in nature. This is engineering– using molecular building blocks to create new biomolecules, such as genes.

Here’s another technique. By comparing the DNA of related species, biologists can work out the DNA structure of their common ancestors.

Then, using synthetic biology, they can reconstruct these sequences in the lab. In this way, biologists have begun to resurrect all kinds of ancient biomolecules, including hormone receptors and even ancient molecular machines.

Today, Betül Kaçar and Eric Gaucher at the Georgia Institute of Technology in Atlanta reveal that they have combined these techniques to perform a remarkable experiment.

These guys have reconstructed an ancient gene from an ancestor of the bacterial organism E coli that lived some 500 million years ago. They’ve then replaced the modern version of this gene with the ancient one in a population of E coli.

“This marks the first time an ancient gene has been genomically integrated in place of its modern counterpart within a contemporary organism,” they say.

This is Jurassic Park on a bacterial scale (although a better name given the timescale might be Cambrian or Ordovician Park).

But Kaçar and Gaucher aren’t finished there. They say their ancient bacteria provide a unique opportunity to replay evolution in the laboratory to see whether today’s E coli evolve all over again or whether something else happens.

The idea is to allow the organism to evolve over many generations in carefully controlled conditions. The various adaptations can be measured using fitness criteria, such as how long it takes for the bacterial population to double. Whole genome sequencing can then show what kinds of changes occur.

This has never been done with bacteria modified in this way. Kaçar and Gaucher say there are essentially two classes of possible outcomes in these experiments.

The first involves the gene itself. Either the ancient gene repeatedly adapts to the modern network to produce an exact copy of its modern counterpart or it evolves in an entirely different way.

The second class involves the network of genes in the modern organism. Either the modern network evolves into the ancient network - thereby resurrecting the ancient creature–or the modern network adapts in an entirely new way.

The problem, of course, will be teasing apart all of this from the messy experimental details.

So far Kaçar and Gaucher have only carried out preliminary fitness measurements. They say the population of ancient E coli takes twice as long to double in size as the modern creatures. But its still early in their work on experimental evolution.

The new approach opens up the possibility of examining all kinds of interesting questions about the role in evolution of factors such as chance and determinism.

For example Kaçar and Gaucher want to know whether evolution leads to single point or to multiple solutions; whether certain mutations are predictable and whether universal laws govern biological evolution.

Those are the kind of questions that will help us understand not only the role of evolution in producing life-as-we-know-it but the role it may play in life-is-we’ve-never-imagined-it; in other words for life on other planets and in artificial life forms yet to be created in the lab.

Important questions from work that will be worth watching in future.

Ref: arxiv.org/abs/1209.5032: Towards the Recapitulation of Ancient History in the Laboratory: Combining Synthetic Biology with Experimental Evolution